Re: Tuning for PostGreSQL Database

From: Terry Lambert (tlambert2_at_mindspring.com)
Date: 07/23/03

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    Date: Tue, 22 Jul 2003 23:21:50 -0700
To: Christopher Weimann <cweimann@k12hq.com>

    Christopher Weimann wrote:
    > On Sun 07/20/2003-01:53:39PM -0700, Sean Chittenden wrote:
    > > You might want to get in the habit of using sysctl for getting that
    > > kind of info. `sysctl -d vfs.bufspace`
    >
    > I'm confused. Everything I have ever read about FreeBSD indicates
    > that it uses all free ram for the disk cache.

    FreeBSD uses all unwired free memory for caching. Wired free
    memory has, by definition, been committed to a type-stable zone,
    and is therefore unavailable for reallocation, since it may have
    been (probably *has* been) fragmented into sub-page-size fragments
    that cannot be recoelesced into pages, even if they are all free,
    so that they can be given back to the system.

    There are some types of kernel allocations that are recoverable
    (e.g. buffer cache entries/VM), but most allocations use the zone
    allocator, and once it owns a page's soul, that page belongs to
    it forever.

    You should read Matt Dillon's excellent VM articles in the Blue
    Prints column at http://www.daemonnews.org/ for more information.

    -- Terry
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